• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.249-252
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• 2003

Acoustic behavior in combustion chamber with acoustic cavity is numerically investigated by adopting linear acoustic analysis. Helmholtz-type resonator is employed as a cavity model to suppress acoustic instability. The tuning frequency of acoustic cavity is adjusted by varying the sound speed in acoustic cavity. Acoustic pressure responses of chamber to acoustic oscillating excitation are shown md acoustic damping effect of acoustic cavity is quantified by damping factor. As the tuning frequency approaches the target frequency of the resonant mode, mode split from the original resonant mode to lower and upper modes appears and thereby damping effect is degraded. Considering mode split and damping effect as a function of tuning frequency, it is desirable to make acoustic cavity tuned to maximum frequency of those of the possible splitted upper modes.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.3
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• pp.240-247
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• 2009

In this paper, we proposed the method of the interference evaluation between the microwave oven noise and the wireless LAN(Local Area Network) by using the GTEM cell. We used microwave oven noise in time to assess the interference unintentional noise effects on wireless LAN and realized by combining an AM(Amplitude Modulation) modulator and a FM(frequency Modulation) modulator. Also the GTEM cell can be used to guarantee the reliability by the evaluations of the frequency and time responses. As measurement results for the APD(Amplitude Probability Distribution) of the interfering noise we analyzed the effect of microwave oven noise to the throughput of wireless LAN.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.1
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• pp.41-48
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• 2022

Vehicle vibration was introduced in the time and frequency domains using fast Fourier transform (FFT) analysis. In particular, a vibration mode analysis and characteristics of the frequency response function (FRF) in a sport utility vehicle (SUV) passing over a bump barrier at different speeds was performed systematically. The response behavior of the theoretical acceleration was obtained using a numerical method applied to the forced vibration model. The amplitude and frequency of the external force on the vehicle cause various power spectra with individual intrinsic system frequencies. In this regard, several modes of power spectra were acquired from the spectra and are discussed in this paper. The proposed technique can be used for monitoring the acceleration in a vehicle passing over a bump barrier. To acquire acceleration signals, various experimental runs were performed using the SUV. These acceleration signals were then used to acquire the FRF and to conduct mode analysis. The vehicle characteristics according to the vehicle condition were analyzed using FRF. In addition, the vehicle structural system and bump passing frequencies were discriminated based on their power spectra and other FRF spectra.

• The Korean Journal of Rheology
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• v.9 no.4
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• pp.163-173
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• 1997

Polystyrene/polycarbonate 조성이 약 50/50인 3종류의 Poly(carbonate-g-styrene) 공중합체의 동적 탄성율, E*($\omega$)와 동적 스트레인-광학계수 O*($\omega$)을 유리전이 영역부근의 여러온도에서 동시에 측정하여 연구하였다. 두 개의 공중합체는 각각의 스티렌 그라프트쇄 에 5, 10 wt%의 MAH를 함유하고 있다. 이들 공중합체의 E*($\omega$)와 O*($\omega$)완화거동과 그라 프트 공중합체의 상용성과 연관하여 비교 고찰하였다. 공중합체들의 E*($\omega$)는 전형적인 무 정형 고분자의 유리전이 완하거동을 보였으며 정성적인 차이를 발견할수 없었다. 그러나 고 강도의 단일 tan$\delta$분산의 저주파수 영역에 미세분산을 나타내, 공중합체는 2상으로 분리되 어 있음이 추정되엇다. 폴리스티렌 그라프트체에 무수 말레인산 함유량이 증가함에 따라, 저 주파수 영역의 미세피크가 $\alpha$주분산에 병합되어 성분 고분자간의 상호 형동성이 증가함을 알수 있었다. 3공중합체의 유사한 기계적 특성과는 달리, 광학적 완화 스펙트럼 O*($\omega$)는 정 성적으로 명확한 차이를 보여 공중합체들의 광학완화 거동이 명확히 다름을 나타냈다. 기계 적 특성보다는 광학적 특성이 공중합체내의 성분 고분자의 미세한 완하 거동에 훨씬 민감한 응답을나타냈다. 이러한 특성적인 공중합체의 O*($\omega$)차이를 공중합체의 조성단일 고분자 PS, PC의 O*($\omega$)의 가성성을 가정하여 모사하였다 모사에서 구한 광학적 부분 기여 파라메 터를 사용하여 공중합체의 상용성을 고찰하였다.

• Journal of the Earthquake Engineering Society of Korea
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• v.4 no.4
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• pp.53-61
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• 2000

능동 제어기를 설계하기 위해서는 제어대상 구조물의 수학모델의 구해야한다. 그러나, 무한차원의 구조물에 대하여 정확한 모델을 구하는 것은 불가능하므로 유한차원인 저차원화된 모델을 사용하여 제어기를 설계한다. 그러나, 실제 구조물과 저차원화된 모델사이의 오차에 의하여 제어기의 성능이 저하가 되면 제어기와 구조물의 상호작용, 지진과 같은 오란 등의 불확실성, 지진시 구조물의 동적 특성 변화로 인하여 제어기의 성능이 더욱 저하가 된다. 이러한 저하 요인은 제어기 설계시 요구되는 구조물의 수학모델에 대한 불확실한 요소로 작용하기 때문에 제어성능의 저하를 일으키며 응답의 불안정을 유발하기로 한다. 본 연구에서는 질량형 능동제어기(AMD)가 설치된 3층 건물 모형의 모델 오차에 관한 불확실성을 반영한 강인제어기법을 적용하여 제어성능과 안정성을 실험을 통하여 분석하였다. 강인제어 기법인 $\mu$ 합성법에 요구되는 여러 가지 가중함수인 주파수필터는 건물과 AMD의 특성, 모델 오차, 제어율과 AMD 성능의 , 측정잡음 및 지진외란의 특성 등을 고려하여 정량적으로 선택되었다. $\mu$합성법에 의하여 제어기를 설계하였으며 강인성을 비교하기 위하여 불확실성이 고려되지 않는 LQG 기법에 의한 제어기를 선택하였다. $\mu$합성법은 규정된 불확성에 대하여 제어의 강인성을 가지므로 동적특성이 바뀐 건물모형에 관한 강인성을 LQG 기법에 의한 제어성능과 비교하였다. 그 결과 동적특성이 변화된 건물에 대하여 $\mu$합성법만이 제어의 효율성이 유지되는 강인성을 나타내었다.

• The Journal of the Acoustical Society of Korea
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• v.26 no.7
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• pp.317-322
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• 2007

This paper is the first step to study on the acoustic characteristics of the Haegeum, a Korean traditional bowed-string instrument. We measured acoustic transfer functions of a Haegeum body using impulse response method. All the measurements are performed in anechoic chamber, INMC, SNU. We examined resonant characteristics of the Haegeum body with obtained transfer functions. Then we performed additional studies which are the Chladni pattern experiments and calculations of air cavity resonances to verify relations between the resonant peaks on the transfer functions and the resonances of each component, such as top plate, air cavity and so on. As a result, we can explain the acoustic characteristics of a Haegeum body and its components.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.154-160
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• 2021

Recently, there have been increasing construction works carried out in urban centers, which are inducing frequent artificial vibration in the vicinity of existing structures due to such construction works. moreover, in case of industrial estates, vibration is induced due to operation of machines in the surrounding areas, thereby causing problems. meanwhile, in case of ordinary concrete that compose structure has low level of damping capability for vibration. accordingly, there are difficulties in blocking a wide range of vibrations delivered to the structures from outside including not only vibrations generated in the structures themselves but also ground vibration. recently, numerous studies are being carried out actively on high-damping system that markedly enhanced the damping performances of structures by utilizing polymer concrete in order to block the vibrations delivered to the structures through ground. therefore, this study compared the performances of polymer concrete with those of ordinary concrete, polyurethane pad and foamed rubber pad in order to review its performances in reducing ground vibration. for this purpose, review of FRF and vibration acceleration as dynamic characteristics was made. after comparative verification on the dynamic characteristics is made when polymer concrete and other aforementioned materials are applied to underground structures, the possibility of application of polymer concrete to structures is reviewed.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.11
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• pp.42-47
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• 2007

In this paper, influence of lossy ground and gap variation between lossy ground and UWB antenna on impulse propagation in time domain for impulse ground penetrating radar (GPR) is numerically and experimentally investigated. For this study, a novel planar UWB fat dipole antenna is developed. First, influence of lossy ground and gap variation between lossy ground and UWB antenna is simulated. For verification, a test field of sand and wet clay soil is built and using the developed dipole antenna, transmission behavior is investigated at the test field. With an aid of IDFT (inverse discrete Fourier transform), time domain impulse response for transmission coefficient measured and simulated in frequency domain is obtained. Measurement and simulation show that the frequency of maximum transmission coefficient and transmission coefficient are increased with higher dielectric constant and larger gap distance. In time domain, it is shown that for higher dielectric constant, the amplitude of the received signal in time domain is higher and reflected signals are seriously modified. Also, it is found that variation of gap between antenna and ground surface makes timing of peak value changed.

• Journal of Sensor Science and Technology
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• v.7 no.5
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• pp.350-355
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• 1998

We fabricated a photoconductive cell made of polycrystalline CdS thick film which has high photo-sensitivity using a print/sintering method. The resultant grain size is about $4\;{\mu}m$. When $CuCl_2$ of 0.06 to 0.12 mg is added, the sensitivity and the ratio of photocurrent to dark current are 0.8 and $10^5$, respectively. The response wavelength is 511 nm. The rise and decay response times are 50 and 20 ms, respectively. In addition, the maximum power dissipation is beyond 80mW. We noticed that the addition of $CuCl_2$ between 0.06 and 0.12 mg to 1g of CdS results in a reliable formation of photoconductive sensor.

• Journal of the Korean Geotechnical Society
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• v.18 no.1
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• pp.101-112
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• 2002

In this study, a new methodology fur the assessment of liquefaction potential is proposed and characteristics of the proposed methodology are verified. The experimental parameter of this methodology, that is, the plastic shear strain trajectory, is compared with the dissipated energy. It is shown that this parameter can express the liquefaction behavior which is generated by excess pore water pressure. This methodology takes advantage of the shear strain time history determined from the site response analysis based on the real time history of earthquake. In this site response analysis, shock type and vibration type records of similar predominant frequency are inputted. The liquefaction safely factors based on the proposed methodology and Korean detailed assessment related to the classical method are calculated from the results of the site response analysis and laboratory dynamic tests. Through this study, it is found that the proposed methodology can not only simulate the liquefaction behavior of saturated soils hut also express the seismic characteristics reasonably : leading type, predominant frequency, maximum acceleration, duration time.